Subject: Hayabusa-2's Odyssey: The First Leg
From: Daniel Adamo <[email-masked]>
Date: Fri, 02 Jan 2015 11:36:40 -0700

ATIG Members-

Happy 2015!  Japan's Hayabusa-2 robotic mission to visit and retrieve
samples from near-Earth asteroid (162173) 1999 JU3 began with launch on 2014
Dec 3.  The attached Sun-centered inertial plot illustrates coasted
Hayabusa-2 motion during the first year following launch, together with that
of Earth and Venus.

The initial solar orbit for Hayabusa-2 has a semi-major axis of 1.002 AU,
bringing it near to Earth a year after launch, as seen in the attached plot.
Thanks to Hayabusa-2's ion thrusters, the plot's coasted trajectory is to
undergo progressive modification in the coming months such that a close
encounter with Earth will occur in late 2015.

Orientation of a Sun-centered orbit plane can be specified by its
inclination with respect to the ecliptic (IN) and by ecliptic longitude of
its ascending node (ELAN).  In the attached plot, Earth's orbit coincides
with the ecliptic plane, and the arrow pointing rightward from the Sun
annotates the direction toward zero ecliptic longitude. The following table
indicates Hayabusa-2's current orbit is very nearly coplanar with that of
1999 JU3.

Orbit        IN (deg)   ELAN (deg)
Hayabusa-2   6.8        250.5
1999 JU3     5.9        251.6

As dotted blue lines projecting position onto the ecliptic plane indicate in
the attached plot, Hayabusa-2's current descending node is very close to the
ecliptic longitude Earth occupies around December 3.  On 2015 Dec 3.0 UTC,
Earth's ecliptic longitude will be 70.259 deg, very near the descending node
for 1999 JU3 (251.6 - 180 = 71.6 deg).

Current perihelion distance for Hayabusa-2 is 0.915 AU, again very close to
1999 JU3's value of 0.963 AU.  Thus, the gravity assist imparted to
Hayabusa-2 from a properly targeted Earth encounter around 2015 Dec 3.0 UTC
will easily enable rendezvous with 1999 JU3, currently set for July 2018.
The precise rendezvous date is largely dependent on how closely the
trajectory following Earth gravity assist matches 1999 JU3's semi-major axis
of 1.190 AU and on how aggressively this residual is reduced by ion
propulsion.

All Hayabusa-2 and 1999 JU3 data provided in this narrative and its attached
plot are traceable to JPL's Horizons server.  This facility is accessible at
http://ssd.jpl.nasa.gov/?horizons.

-Dan